Medical devices comprising catheter shafts and catheter balloons are used in an increasingly widening variety of applications including vascular dilatation, stent delivery, drug delivery, delivery and operation of sensors and surgical devices such as blades, and the like. The desired physical property profile for the balloons used in these devices vary according to the specific application, but for many applications a high strength robust balloon is necessary and good softness and trackability properties are highly desirable.
Commercial high strength balloons having wall strengths in excess of 20,000 psi, have been formed of a wide variety of polymeric materials, including PET, nylons, polyurethanes and various block copolymer thermoplastic elastomers. U.S. Pat. No. 4,490,421, Levy, and U.S. Pat. No. 5,264,260, Saab, describe PET balloons. U.S. Pat. No. 4,906,244, Pinchuk et al, and U.S. Pat. No. 5,328,468, Kaneko, describe polyamide balloons. U.S. Pat. No. 4,950,239, Gahara, and U.S. Pat. No. 5,500,180, Anderson et al describe balloons made from polyurethane block copolymers. U.S. Pat. No. 5,556,383, Wang et al, and U.S. Pat. No. 6,146,356, Wang et al, describe balloons made from polyether-block-amide copolymers and polyester-block-ether copolymers. U.S. Pat. No. 6,270,522, Simhambhatla, et al, describes balloons made from polyester-block-ether copolymers of high flexural modulus. U.S. Pat. No. 5,344,400, Kaneko, describes balloons made from polyarylene sulfide. U.S. Pat. No. 5,833,657, Reinhart et al, describes balloons having a layer of polyetheretherketone. All of these balloons are produced from extruded tubing of the polymeric material by a blow-forming radial expansion process. U.S. Pat. No. 5,250,069, Nobuyoshi et al, U.S. Pat. No. 5,797,877, Hamilton et al, and U.S. Pat. No. 5,270,086, Hamlin, describe still further materials which may be used to make such balloons.
A variety of blow forming techniques have been utilized. The extruded parison may be radially expanded as is into a mold or by free-blowing. Alternatively, the parison may be pre-stretched longitudinally before expansion or reformed in various ways to reduce thickness of the balloon cone and waist regions prior to radial expansion. The blowing process may utilize pressurization under tension, followed by rapid dipping into a heated fluid; a sequential dipping with differing pressurization; a pulsed pressurization with compressible or incompressible fluid, after the material has been heated. Heating may also be accomplished by heating the pressurization fluid injected into the parison. Examples of these techniques may be found in the patent documents already mentioned or in U.S. Pat. No. 4,963,313, Noddin et al, U.S. Pat. No. 5,306,246 Sahatjian, U.S. Pat. No. 4,935,190, Tennerstedt, U.S. Pat. No. 5,714,110, Wang et al, U.S. Pat. No. 5,304,340, Downey.
Following blow-forming the balloons may be simply cooled, heat set at a still higher pressure and/or temperature or heat shrunk at an intermediate pressure and/or temperature, relative to the blow forming temperature and pressure. See U.S. Pat. No. 5,403,340, Wang et al; EP 540858, Advanced Cardiovascular Systems, Inc.; and WO 98/03218, Scimed Life Systems.
In commonly owned copending U.S. application published as U.S. 2003-0167067 A1, Wang et al., incorporated herein by reference, it is disclosed that improved balloon properties can be obtained by controlling the parison extrusion in a manner which restricts the elongation of the parison material in the longitudinal direction.
U.S. Pat. No. 5,714,110, Wang et al., describes a method for forming a catheter balloon comprising the steps of placing tubing of a thermoplastic material in a mold and blowing the balloon by pressurizing and tensioning the tubing while gradually dipping the mold into a heated heat transfer media so as to sequentially blow the first waist, the body and the second waist portions of the balloon, the tubing being subjected to a relatively lower pressure while the body portion is blown than while the first and second waist portions are blown.
In commonly owned copending U.S. application Ser. No. 10/617,428, filed Jul. 7, 2003, Schewe, et al, entitled “Medical Device Tubing With Discrete Orientation Regions”, methods of forming extruded tubular polymeric segments with a varied orientation or elongation along the length thereof are disclosed.
In U.S. Pat. No. 6,572,813, Zhang et al, an apparatus is described in which a mold form is heated by mechanically moving one or more external heaters along the outside of a balloon mold containing a tubular parison. The document states that the temperature of the parison, along the effective length of the mold should be kept within a specified minimum difference, for instance 100° C. and preferably within 20° C. That is, a relatively non-uniform heating apparatus is controlled to provide a more uniform heating. In this respect the system is understood to merely mimic heating behaviour of well known balloon molding systems, for instance those in which mold forms are dipped into a heated liquid bath and those in which a block heater surroundingly contacts the mold.
In mass production of medical device balloons, some processes produce substantial rejection rates. Parison shaping techniques going beyond simple axial stretching and radial expansion of straight tubes tend to increase balloon rejection rates. Grinding or necking down ends of a parison may have such an effect. Nevertheless, shaped parisons are often needed, for instance to allow large diameter balloons to be fashioned with high burst strength and/or for mounting on small diameter catheters. A free-blowing step in a balloon forming process can also display such problems.
Process improvements in the balloon forming art which minimize rejection rates are desirable both for the direct reduction in manufacturing cost and for the reduced likelihood that a defective balloon will escape inspection. Consequently there is ongoing need for process improvements in the medical balloon forming arts.